Sepsis is a syndrome of infection and systemic inflammation that is a top 10 cause of death with increasing incidence affecting approximately 2 million Americans yearly. The inflammatory, hemodynamic, and metabolic abnormalities that characterize sepsis are also known triggers and risk factors for atrial fibrillation. Atrial fibrilation is a heart rhythm disturbance characterized by a loss of normal atrial contractility and rapid heart rates. The hypothesis that sepsis is a strong atrial fibrillation trigger is supported by the observation that patients hospitalized with severe sepsis (vs. non-severe sepsis) have a 6-fold increased risk of developing new-onset atrial fibrillation. Importantly, patients who develop new-onset AF during severe sepsis have significantly increased risk for in-hospital death and stroke. More than 1/2 of patients who develop atrial fibrillation during severe sepsis do not survive to hospital discharge. No data are available for prognostication of long term outcomes in patients with sepsis-associated, new-onset atrial fibrillation. Further, little evidence exists to weigh riss and benefits of complicated treatment decisions for atrial fibrillation during sepsis. In line with the National Heart, Lung, and Blood Institute's mission to promote the prevention and treatment of heart, lung, and blood disease, the current proposal will use complementary administrative claims data sources to determine long-term outcomes and compare effectiveness of practice patterns associated with new-onset atrial fibrillation occurring during sepsis. Through the Mentored Career Development Award, the candidate will develop skills necessary for transition to an independent research career, including training in advanced epidemiologic methods, health services/outcomes/observational comparative effectiveness research methods, advanced biostatistics/data management techniques, and development of leadership and writing expertise. The information produced from the proposed project will inform further comparative effectiveness and efficacy trials designed to directly inform clinical decisions for patients with atrial fibrillation during sepsis. In addition, the career development and training skills learned during the award will allow the candidate to build and expand upon the currently limited data sources available for the study of patients with sepsis.